1. Field of the Invention
This invention relates to a camera module, and more specifically to a camera module that can be used in small-sized electronic apparatuses such as digital cameras, camera-equipped cellular phones and the like.
2. Description of the Prior Art
A camera module having a function of displacing a lens unit in a direction of an optical axis of the lens unit is used in relatively small-sized digital cameras, camera-equipped cellular phones and the like. This function is used for providing an autofocus function and/or zoom function and the like, and is achieved by an interaction between a magnetic field generated by an electrical current flowing in a coil and a magnetic field generated by a yoke and magnets provided on the yoke.
Such a camera module includes a barrel which holds the lens unit, a holder which houses the barrel therein, and a pair of leaf springs for supporting the holder so that the holder is displaceable in a direction of an optical axis of the lens unit.
FIG.10 is an exploded perspective view of an autofocus actuator assembly 100 used in a conventional camera module for displacing a lens unit 115 in a direction of an optical axis thereof. It is to be noted that an imaging element 117 on substrate 116 is provided below a base 111 of the actuator assembly 100.
A holder 108 that houses a barrel (not shown) holding the lens unit is provided between a cover 101 and the base 111 so that the holder 108 is displaceable in a direction of an optical axis of the lens unit together with the lens unit.
A ring-shaped inner annular portion 104b of an upper leaf spring 104 and a ring-shaped inner annular portion 110b of a lower leaf spring 110 are attached to the upper and lower cylindrical end portions of the holder 108, respectively, using an adhesive. Further, a ring-shaped outer annular portion 104a of the upper leaf spring 104 is attached to a top surface of a yoke 105 which is mounted on the base 111 and a ring-shaped outer annular portion 110a of the lower leaf spring 110 is attached to the base 111, respectively.
Three bridge portions 104c are coupled between the outer annular portion 104a and the inner annular portion 104b of the upper leaf spring 104. As is the same with the upper leaf spring 104, three bridge portions 110c are coupled between the outer annular portion 110a and the inner annular portion 110b of the upper leaf spring 110. By resilient deformation of the respective three bridge portions 104c and 110c, the holder 108 can be displaced in a direction of an optical axis of the lens unit.
A plurality of magnets 106 are provided on the yoke 105 so as to produce a magnetic field. The yoke 105 has an axial bore 105a for receiving the holder 108. Further, a coil 107 is provided around an outer periphery of the holder 108 so that the coil 7 is disposed in the magnetic field produced by the magnets and the yoke 105 in a state that the holder 108 is received in the axial bore 105a. By supplying a current to the coil 107 to generate a magnetic field, the holder 108 can be displaced in a direction of an optical axis of the lens unit by a driving force generated by the interaction of the magnetic fields. In this regard, it is to be noted that a component denoted by the reference numeral 103 is a flexible printed circuit board used for supplying a current to the coil 107, a component denoted by the reference numeral 102 is a stopper arranged above the upper surface of the inner annular portion of the upper leaf spring 104, and a component donated by the reference numeral 109 is a ring-shaped plate provided between the lower leaf spring 110 and the bottom surface of the yoke 105.
It is to be noted that an actuator assembly similar to the actuator assembly 100 having such upper leaf spring 104 and lower leaf spring 110 described above is disclosed in JP-A-No.2004-280031.
As described above, the upper leaf spring 104 and the lower leaf spring 110 are bonded to the upper and lower cylindrical end portions of the holder 108, respectively, using an adhesive. In this case, a synthetic resin (e.g. epoxy resin) is used as the adhesive. Such a synthetic resin is applied onto an end surface of each of the upper and lower cylindrical portions of the holder 108 by hand of a worker. However, the width of the end surface of the cylindrical end portion is extremely narrow. Therefore, an application of the synthetic resin to the end surface must be carried out carefully, and thus there is a problem in that a time required for the application operation cannot be shortened. Further, an additional time is required for waiting the hardening of the applied synthetic resin, that is, it is necessary to leave the holder 108 to which the synthetic resin has been applied as it is for a certain period of time after completion of the application of the synthetic resin. This leads to another problem in that a time required for manufacturing the camera module cannot be shortened.
Furthermore, in the case where a bonding area, that is an area of the end surface of the holder is extremely small, or in the case where a bonding condition of the synthetic resin against the inner annular portion of the leaf spring is not sufficient, it is not possible to ensure a sufficient bonding strength therebetween. In such a case, there is a problem in that the upper leaf spring 104 and/or the lower leaf spring 110 may be partially peeled off from the holder 108 due to the reduced bonding force in the event that the electronic apparatus equipped with the camera module is dropped by accident.